1. Field of the Invention
This invention relates generally to the field of packaging, and more specifically to the field of blow molded plastic containers for packaging substances such as beverages.
2. Description of the Related Technology
Many products that were previously packaged using glass containers are now being supplied in plastic containers. Polyethylene terephthalate (PET) thermoplastic resins are polyester materials that provide clarity and transparency that is comparable to glass. PET possesses the processing characteristics, chemical and solvent resistance and high strength and impact resistance that are required for packaging products such as juices, soft drinks and water. PET containers are lightweight, inexpensive, and recyclable and can be economically manufactured in large quantities. They will not shatter and create potentially dangerous shards when dropped, as glass containers may.
PET containers have conventionally been manufactured using the stretch blow molding process. This involves the use of a pre-molded PET preform having a threaded portion and a closed distal end. The preform is first heated and then is longitudinally stretched and subsequently inflated within a mold cavity so that it assumes the desired final shape of the container. As the preform is inflated, it elongates and stretches, taking on the shape of the mold cavity. The polymer solidifies upon contacting the cooler surface of the mold, and the finished hollow container is subsequently ejected from the mold.
In order to minimize materials costs, a plastic container should ideally be constructed to use as little plastic resin as possible. Such lightweighting is usually accomplished by making the sidewall of the container as thin as possible, but this adversely impacts the strength and rigidity of the sidewall. In larger plastic beverage containers, such as those having a volumetric capacity of 64 ounces or greater, outward bulging of the sidewall as result of the hydrostatic pressure exerted by the liquid within the container can be problematic, particularly in containers that are noncircular in transverse cross-section.
A need has existed for an improved noncircular plastic container that possesses improved resistance to outward bulging of the sidewall with respect to conventional containers, without having a significant negative impact on material costs.